The present invention relates to X-ray photography cassettes in which a rear cover is coupled through hinges to a body with a front plate and intensifying screens are held upon the inner surfaces of the front plate and the rear cover. More particularly, the invention relates to an X-ray photography cassette in which a loaded film having a tendency to stick onto the intensifying screens can be peeled off.
For high sensitivity, X-ray photography is carried out with a film sandwiched between two intensifying screens. If the film is placed in close contact with the intensifying screens, the taken picture will have a quite excellent sharpness. An X-ray photography cassette in which the rear cover is coupled through hinges to the body has been extensively employed because the film can be loaded and unloaded automatically and mechanically as well as manually. The curvature of the rear cover and the quality and the thickness distribution of the corresponding depressing material such as a sponge material interposed between the rear cover and the intensifying screen are determined so that the film is maintained in close contact with the intensifying screen by the pressure between the front plate and the rear cover which results when the rear cover is closed.
The film and the intensifying screen thus held in close contact with each other tend to stick to each other because of vacuum conditions, humidity or static electricity. This tendency increases as the contact between the film and the intensifying screen increases. Therefore, such an X-ray photography cassette suffers from a defect in that it is difficult to peel the film off the intensifying screen when the film is taken out of the cassette.
For a film unloading apparatus which automatically takes out the film which has been loaded in the X-ray photography cassette and exposed to X-rays and delivers it to an automatic developing machine or the like, a system is employed in which the X-ray photography cassette is loaded in the cassette loading section of the apparatus with the rear cover held under it and the loaded film is allowed to drop by its own weight (hereinafter referred to as "a gravity drop system" when applicable) when the rear cover is opened. The mechanism and operation of this device are very simple. In taking the film out of the cassette using the gravity drop system, as described above, sometimes the film sticks onto the intensifying screen because of vacuum, humidity or static electricity. For eliminating this difficulty, the present applicant earlier proposed a cassette cover opening mechanism as disclosed in Japanese Utility Model Application No. 45067/1975 in which means for vibrating the body and the rear cover of a cassette after its cover has been opened is provided.
Furthermore, known in the art is an X-ray photography cassette which has a cut-out portion which forms an air pool in order to peel the film off the intensifying screen by negative pressure which is created when the cover of the cassette is opened. Such a cassette is described in Japanese Utility Model Application No. 121247/1972 also filed by the present applicant. If these techniques are employed, in almost all cases the film can be peeled off the intensifying screen and dropped from the cassette. However, sometimes the film sticks onto the intensifying screen on the rear cover which results in it taking a relatively long time to peel the film off the intensifying screen.
Examples of a conventional cassette including means for peeling film which is stuck onto an intensifying screen retained on the cassette utilizing spring means are disclosed in Japanese Utility Model Application Publication No. 29981/1964 which describes the use of an elastic plastic material such as a foamed plastic material provided in a cut-out portion formed in the intensifying screen on the body side so that the elastic plastic material is depressed and contracted when the rear cover is closed and that the elastic plastic material raises the film to peel it off the intensifying screen when the rear cover is opened.
However, these conventional cassettes are still disadvantageous in the following points. Since the spring means or the elastic plastic material protrudes from the surface of the intensifying screen when the rear cover is opened, the end of the film tends to be caught by the spring means or the elastic plastic material or the film is lifted so as to make it impossible to stably position the film while automatically loading the film in the cassette. Furthermore, in a cassette in which the film is maintained energized so as to be repelled from the intensifying screen, contact between the film and the intensifying screen is reduced.
In addition, a cassette is known in which, as described in U.S. Pat. Nos. 3,504,180 and 3,511,990, the intensifying screen is bent to peel the film off the intensifying screen when the cover is opened. However, this cassette construction is disadvantageous in that the construction of the cassette is intricate and the durability of the intensifying screen is adversely affected.
Accordingly, an object of the present invention is to provide an X-ray photography cassette in which a film can be smoothly loaded, the film is maintained in close contact with the intensifying screen when the rear cover is closed, and the film can be easily peeled off the intensifying screen when the rear cover is opened to take the film out of the cassette.